On 11/07/2017 11:43, Stefan Hajnoczi wrote: >>> >>> 1. Must be called under BQL? >>> 2. Can I/O requests be in flight? >>> 3. Is it thread-safe? >>> >>> Otherwise it will be a nightmare to modify the code since these >>> constraints are not enforced by the compiler and undocumented. >> Good point. Are (1) and (3) different ways to say the same thing or do >> you have other differences in mind? > There is a difference between (1) and (3). If a function is thread-safe > then callers can invoke it without any constraints. If a function > requires a specific lock to be held then that it puts a constraint on > the caller. > > We do have thread-safe functions in the block layer: simple functions > that fetch a BDS field atomically. There is no need to hold the BQL for > them.
Ok, so we are in (somewhat violent) agreement. "It's not thread-safe" pretty much means "must be called under BQL". I look forward to extending Marc-André's -Wthread-safety experiments to cover bdrv_drained_begin/end! Paolo
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